This invention relates to oscillating jets.
Oscillating jets are jets that are excited to exhibit dynamic modes of oscillation. While oscillating jets may potentially be excited to exhibit diverse modes of oscillation, illustrative examples of oscillating jets include the xe2x80x9cflapping jetxe2x80x9d wherein the jet column xe2x80x9cflapsxe2x80x9d from side to side in a quasi-planar fashion, and the xe2x80x9cprecessing jetxe2x80x9d wherein the jet column rotates (or xe2x80x9cprecessesxe2x80x9d) as a whole about an axis other than its own.
Oscillating jets, such as the precessing jet and the flapping jet, have broad potential industrial applicability in the mixing of fluids due to their enhanced mixing characteristics relative to conventional non-oscillating jets. Examples of industrial processes in which oscillating jets have potential applicability include combustion systems, chemical reactors, heat and mass exchangers, fluid mixers, and spray systems.
The potential widespread practical application of oscillating jets to mix fluids has at least partially been facilitated by the development of simple fluidic devices capable of exciting oscillating jets. For example, the present applicant""s international patent publication WO88/08104 discloses several simple fluidic devices capable of exciting an oscillating jet without acoustic or mechanical excitation techniques. Specifically, the fluidic devices disclosed in WO88/08104 use the separation of a primary flow in a chamber to excite a large-scale, low frequency precessing jet.
While industrial application of the fluidic devices disclosed in WO88/08104 as burners in rotary cement kilns has demonstrated that a gas precessing jet flame is highly stable and significantly reduces Nox emissions relative to conventional non-oscillating flames, the broader industrial application of the precessing jet has been hindered by the absence of a capability to manipulate and regulate directly the evolution and mixing characteristics of the jet. In this regard, it will be appreciated that the ability to adapt and regulate the mixing characteristics of a jet is essential if the performance of the jet is to be optimised for any given industrial application.
The above example of the precessing jet clearly illustrates that the broad industrial application of oscillating jets generally is not merely contingent upon the development of simple fluidic devices, but also upon the development of a capability whereby the evolution and mixing characteristics of the oscillating jets excited by such devices can be simply and readily adapted to mix fluids in a predetermined manner that is optimal for any given industrial process.
Several fluidic devices have been proposed in the present applicant""s international patent publications WO94/07086 and WO96/27761 to address the above technical problem in the context of the precessing jet burners. These fluidic devices are improvements of the fluidic devices disclosed in WO88/08104 wherein a precessing jet flame is combined with a closely proximate non-oscillating jet flame is used to influence the characteristics of the combined flame. While the fluidic devices disclosed in WO94/07086 and WO96/27761 advantageously enhance the performance of the precessing jet in combustion systems such as rotary cement kilns, they do not directly facilitate the optimisation of the performance of the precessing jet for other specific industrial applications because they do not provide the capability of direct, simple adaptation and regulation of the mixing characteristics of the precessing jet itself.
Against the above background, the present applicant has determined that a requirement exists for a simple fluidic device for exciting an oscillating jet whose mode of oscillation and mixing characteristics can be determined such that the performance of the oscillating jet can be optimised for any given industrial application. Importantly, the device should not only be capable of exciting the above illustrative examples of the flapping jet and the processing jet, but a broad range of oscillating jets whose particular dynamic modes of oscillation and mixing characteristics are optimal for specific industrial applications.
In general, according to a first aspect of the present invention, there is provided a method of producing a fluidic device for exciting an oscillating jet having predetermined characteristics, the fluidic device including a chamber having a fluid inlet such that in use fluid entering the chamber through the fluid inlet separates from the inner surface of the chamber to excite an oscillating jet, the method including the step of:
configuring the geometry of the fluid inlet to determine the mode of oscillation and mixing characteristics of the oscillating jet.
Advantageously, the mode of oscillation and mixing characteristics of the oscillating jet excited by the fluidic device are determined by selectively configuring the geometry of the cross-section of the fluid inlet. Advantageously, the geometry of the cross-section of the fluid inlet is non-circular and is selectively configured to be triangular, rectangular, polygonal or elliptical (other geometric plane figures such as crosses and stars may be used with advantage in some embodiments). Advantageously, the geometry of the cross-section of the fluid inlet may be further selectively configured by varying dimensions of the cross-section of the fluid inlet.
In another aspect, the present invention provides a fluidic device for exciting an oscillating jet whose characteristics can be determined to meet operational requirements, the fluidic device including a chamber having a fluid inlet such that in use fluid entering the chamber through the fluid inlet separates from the inner surface of the chamber to excite an oscillating jet, wherein means are provided to vary the geometry of the fluid inlet such that the mode of oscillation and mixing characteristics of the oscillating jet can be determined to meet operational requirements.
Advantageously, the means provided to vary the geometry of the fluid inlet comprise a plurality of elements that may be alternatively removably positioned inside the chamber, each of the elements being provided with an orifice that constitutes the fluid inlet when the respective elements are removably positioned in the chamber. Advantageously, the orifices of the respective elements possess different geometries. Advantageously, the orifices provided in the respective elements are non-circular in cross-section. Accordingly, the shape of the cross-section of the orifice may be selected to be triangular, rectangular, polygonal, or elliptical (other geometric plane figures such as crosses and stars may be used with advantage in some embodiments).
Conveniently, once the fluidic device has been installed for service in a particular industrial application, the geometry of the fluid inlet can be simply and readily varied by substituting one element for another having a differently configured orifice. It will be appreciated from the above method of the present invention that the selective variation of the geometry of the fluid inlet facilitates the manipulation and regulation of the mode of oscillation and mixing characteristics of the oscillating jets excited by the fluidic device. Accordingly, the performance of the oscillating jet excited by the fluidic device can be optimised and/or varied to meet the specific service requirements of any given practical application.
As an alternative to the use of removably positionable orifices, means could be integrally provided in the fluidic device to vary the geometry of the fluid inlet in situ by mechanical or fluidic means such that the mode of oscillation and mixing characteristics of the oscillating jet can be determined to meet operational requirements.